P-P Condensation and P-N/P-P Bond Metathesis: Facile Synthesis of Cationic Tri- and Tetraphosphanes

[LC R P((PhP)2 C2 H4 )][OTf] (4 a,b[OTf]) and [LC iPr P(PPh2 )2 ][OTf] (5 b[OTf]) were prepared from the reaction of imidazoliumyl-substituted dipyrazolylphosphane triflate salts [LC R P(pyr)2 ][OTf] (3 a,b[OTf]; a: R=Me, b=iPr; LC R =1,3-dialkyl-4,5-dimethylimidazol-2-yl; pyr=3,5-dimethylpyrazol-1-yl) with the secondary phosphanes PhP(H)C2 H4 P(H)Ph) and Ph2 PH. A stepwise double P-N/P-P bond metathesis to catena-tetraphosphane-2,3-diium triflate salt [(Ph2 P)2 (LC Me P)2 ][OTf]2 (7 a[OTf]2 ) is observed when reacting 3 a[OTf] with diphosphane P2 Ph4 . The coordination ability of 5 b[OTf] was probed with selected coinage metal salts [Cu(CH3 CN)4 ]OTf, AgOTf and AuCl(tht) (tht=tetrahydrothiophene). For AuCl(tht), the helical complex [{(Ph2 PPLC iPr )Au}4 ][OTf]4 (9[OTf]4 ) was unexpectedly formed as a result of a chloride-induced P-P bond cleavage. The weakly coordinating triflate anion enables the formation of the expected copper(I) and silver(I) complexes [(5 b)M(CH3 CN)3 ][OTf]2 (M=Cu, Ag) (10[OTf]2 , 11[OTf]2 ).

The atomic level mechanism of white phosphorous demolition by di-iodine

A detailed mechanism of the I₂-induced transformation of white phosphorus into PI₃ emerges from a DFT analysis. This multi-step process implies that at any stage one P-P and two I-I bonds cleavages, associated with the formation of two P-I bonds plus an in situ generated brand new I₂ molecule. Significant electron transfer between the atoms is observed at any step, but the reactions are better defined as concerted rather than redox. Along the steepest descent to the product, no significant barrier is encountered except for the very first P₄ activation, which costs +14.6 kcal mol^-1. At the atomic level, one first I₂ molecule, a typical mild oxidant, is first involved in a linear halogen bonding interaction (XB) with one P donor, while its terminal I atom is engaged in an additional XB adduct with a second I₂. Significant electron transfer through the combined diatomics allows the external I atom of the dangling I₃ grouping to convey electrons into the σ* level of one P-P bond with its consequent cleavage. This implies at some point the appearance of a six-membered ring, which alternatively switches its bonding and no-bonding interactions. The final transformation of the P₂I₄ diphosphine into two PI₃ phosphines is enlightening also for the specific role of the I substituents. In fact, it is proved that an organo-diphosphine analogue hardly undergoes the separation of two phosphines, as reported in the literature. This is attributable to the particularly high donor power of the carbo-substituted P atoms, which prevents the concertedness of the reaction but favors charge separation in an unreactive ion pair.

Unexpected Reactivity of [(η(5) -1,2,4-tBu3 C5 H2 )Ni(η(3) -P3 )] towards Main Group Nucleophiles and by Reduction

The reduction of [Cp'''Ni(η(3) -P3 )] (1; Cp'''=η(5) -1,2,4-tBu3 C5 H2 ) with potassium produces the complex anion [(Cp'''Ni)2 (μ,η(2:2) -P8 )](2-) (2), which contains a realgar-like P8 unit. The anionic triple-decker sandwich complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )](-) (3) with a cyclo-P3 middle deck is obtained when 1 is treated with NaNH2 as a nucleophile. Na[3] can subsequently be oxidized with AgOTf to the neutral triple-decker complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )] (4). In contrast, 1 reacts with LiPPh2 to give the anionic compound [(Cp'''Ni)2 (μ,η(2:2) -P6 PPh2 )](-) (5), a complex containing a bicyclic P7 fragment capped by two Cp'''Ni units. Protonation of Li[5] with HBF4 leads to the neutral complex [(Cp'''Ni)2 (μ,η(2:2) -(HP6 PPh2 )] (6). Adding LiNMe2 to 1 results in [Cp'''Ni(η(2) -P3 NMe2 )](-) (7) becoming accessible, a complex which forms as a result of nucleophilic attack at the cyclo-P3 ring of 1. The complexes K2 [2], Na[3], 4, 6, and Li[7] were fully characterized and their structures determined by single-crystal X-ray diffraction.

Recent highlights in mixed-coordinate oligophosphorus chemistry

This review aims to highlight and comprehensively summarize recent developments in the field of mixed-coordinate phosphorus chemistry. Particular attention is focused on the synthetic approaches to compounds containing at least two directly bonded phosphorus atoms in different coordination environments and their unexpected properties that are derived from spectroscopic and crystallographic data. Novel substance classes are discussed in order to supplement previous reviews about mixed-coordinate phosphorus compounds.

Formation of the spirocyclic, Si-centered cage cations [ClP(NSiMe3)2Si(NSiMe3)2P5](+) and [P5(NSiMe3)2Si(NSiMe3)2P5](2)

On account of our interest in P4 activation by phosphenium ion insertion into P-P bonds we have developed synthetic routes to bicyclic N-P-Si-heterocycle 7 and probed its reactivity towards GaCl3 and P4. A GaCl3-induced rearrangement of 7 leads to the in situ formation of spirocyclic, Si-centered phosphenium ions. Their insertion into P-P bonds of one or two P4 tetrahedra yields polyphosphorus cages [ClP(NSiMe3)2Si(NSiMe3)2P5](+) (19(+)) and [P5(NSiMe3)2Si(NSiMe3)2P5](2+) (13(2+)).

[(ClImDipp)PP(Dipp)][GaCl4]: a polarized, cationic diphosphene

The reaction of neutral diphosphanide [(^ClIm^Dipp)P–P(Cl)(Dipp)] with the Lewis acid GaCl₃ yields cationic diphosphene [(^ClIm^Dipp)PP(Dipp)]⁺, which is explained by a low P–Cl bond dissociation energy. The polarized PP double bond in [(^ClIm^Dipp)PP(Dipp)]⁺, allows for its utilization as acceptor for nucleophiles, such as Cl⁻ or PMe₃.

From the parent phosphinidene–carbene adduct NHCPH to cationic P4-rings and P2-cycloaddition products

The parent phosphinidene–carbene adduct NHCPH reacts with chlorophosphanes yielding NHC-supported chlorodiphosphanes, which can be transformed to novel P₄-rings and reactive 1,2-diphosphenes.

Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and EV cations

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized.

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized. The unique molecular and electronic structures of this new class of complexes involving pnictogen Lewis acids has been assessed in the solid, solution and gas phases to reveal systematic variations in metric parameters, ligand lability and charge concentration. While the Lewis acidity of E³⁺ has the trend E = Bi < Sb < As < P as determined by gas-phase calculations and ¹H NMR spectroscopy, the Lewis acidity of [6E]³⁺ has the trend E = P < As < Sb < Bi according to gas-phase calculations. Derivatives of [6′E][OTf]₃ (E = P, As) are latent sources of E(OTf)₃ as demonstrated by their reactions with dmap, which give the corresponding derivatives of [(dmap)₃E][OTf]₃. The highly oxidizing nature of P(OTf)₃ and As(OTf)₃ is evidenced in reactions of [6′E][OTf]₃ (E = P, As) with phosphines, which give E^I-containing monocations [(R₃P)₂E]¹⁺ and oxidatively coupled dications [R₃PPR₃]²⁺, illustrating new P–P and P–As bond forming strategies. Cations [6′E]³⁺ (E = P, As) are C–H bond activating agents that dehydrogenate 1,4-cyclohexadiene, with higher activity observed for E = P. Combinations of [6′E]³⁺ and ^tBu₃P activate H₂ and D₂ under mild conditions, evidencing frustrated Lewis pair activity. Oxidation of [6′P][OTf]₃ with SO₂Cl₂ gives [(tbbipy)₂PCl₂][OTf]₃, containing a P^V-trication, but there is no evidence of the analogous reaction with [6′As][OTf]₃. The observations highlight new directions in the chemistry of highly charged cations and reveal a rich reactivity for p-block triflates E(OTf)₃, which can be accessed through derivatives of [6E][OTf]₃ and [6′E][OTf]₃.

Low-Temperature Isolation of the Bicyclic Phosphinophosphonium Salt [Mes*2P4Cl][GaCl4]

The reaction of [ClP(μ-PMes*)]2 (1) with the Lewis acid GaCl3 yielded a hitherto unknown tetraphosphabicyclo[1.1.0]butan-2-ium salt, [Mes*P4(Cl)Mes*][GaCl4] (3[GaCl4]), which incorporates a positively charged phosphonium center within its bicyclic P4 scaffold. The formation of the title compound was studied by means of low-temperature NMR experiments. This led to the identification of an intermediate cyclotetraphosphenium cation, which was trapped by reaction with dimethylbutadiene (dmb). All of the compounds were fully characterized by experimental and computational methods.

The chemistry of cationic polyphosphorus cages--syntheses, structure and reactivity

The aim of this review is to provide a comprehensive view of the chemistry of cationic polyphosphorus cages.

The aim of this review is to provide a comprehensive view of the chemistry of cationic polyphosphorus cages. The synthetic protocols established for their preparation, which are all based on the functionalization of P₄, and their intriguing follow-up chemistry are highlighted. In addition, this review intends to foster the interest of the inorganic, organic, catalytic and material oriented chemical communities in the versatile field of polyphosphorus cage compounds. In the long term, this is envisioned to contribute to the development of new synthetic procedures for the functionalization of P₄ and its transformation into (organo-)phosphorus compounds and materials of added value.

Synthesis and onwards coordination of an As(I) centered zwitterion

The bis(phosphino)borate ligand class is used as an anionic anchor to stabilize reactive, low coordinate arsenic centers. The neutral, zwitterionic As(I) species, 2, is formed very cleanly, and isolated in good yields using cyclohexene as a halogen scavenger. The uniqueness of this heterocyclic As(I) compound is on display with the coordination to Group 6 metal centers, (2 M(CO)5; M = Cr, Mo, W). The arsenic-metal bond lengths are longer than the related AsPh3 complexes suggesting that compound 2 is a weak sigma donor. The metal complexes reveal a trigonal pyramidal arsenic atom, which provides the first experimental evidence for the presence of two "lone pairs" of electrons on the As(I) center. When more flexible and more electron-donating isopropyl substituents were used, an intermediate (compound 5) in the formation of low coordinate pnictogen compounds was crystallographically characterized. This structure, formally a base-stabilized dichloroarsenium cation, provides an alternative mechanistic proposal to the one described in the literature.